Injectors are a commonly used device for injecting fuel into the cylinders of an internal combustion engine, as well as injecting diesel exhaust fluid (DEF) into the exhaust flow path, more particularly the exhaust pipe. While DEF alone is not corrosive, DEF has the capacity to support a corrosion reaction due to its conductivity. DEF and condensed diesel exhaust system gases support electrochemical corrosion of stainless steel components within the injector.
Some types of injectors have a ball which is part of a valve, and the ball selectively contacts a valve seat, depending upon whether or not the valve is opened or closed. The injector may include a solenoid portion which actuates the valve. Various parts of the injector are exposed to DEF during operation, such as the ball, and the component used to connect the ball to the solenoid portion. The ball is typically welded to the component which connects the ball to the solenoid portion, and the movement of the solenoid portion controls the movement of the ball. The ball is selectively in contact with the valve seat to change the valve between an open position and a closed position.
In an injector application, it is desirable to have a hard ball to maximize durability. In most cases, hardened 440C stainless steel is used because it is hard, corrosion resistant, and weldable. It is known that welding hardened 440C creates an area known as the heat affected zone (HAZ). In this area, the corrosion resistance is reduced due to migration of the protective chromium to carbon. When this chromium migration occurs, the exposed surface has a dearth of chromium which is the key ingredient in corrosion protection. Materials with low carbon are not affected in this manner, but carbon is the ingredient within steel which provides the desired hardening capability of 440C.
The use of steel balls with 440C hardness is employed extensively for gasoline injectors without corroding, but when used with DEF, corrosion in the HAZ is likely. Several attempts have been made to minimize the corrosion problem by coating the ball with thin protective coatings. The ball does not always get full coverage using this method because the entire area of the ball is not exposed to the carbon during the coating process. Corrosion protection in this instance is therefore unpredictable.
Accordingly, there exists a need for an injector having a ball welded to a tube which is corrosion resistant to DEF and condensed diesel exhaust system gases. More particularly, there is also a need for a ball and tube assembly used as part of a solenoid injector which resists or at least reduces corrosion from DEF and condensed diesel exhaust system gases.